A conventional driving apparatus includes, as disclosed in patent document 1 (JP 2005-73399A), an inverter circuit and a control circuit. The inverter circuit outputs three-phase AC currents to a three-phase AC synchronous motor. The control circuit controls the inverter circuit.
Specifically, the inverter circuit is configured by three sets of a pair of series-connected transistors. The three sets are connected in parallel between a positive bus and a negative bus. A direct current (DC) power source is connected between the positive bus and the negative bus. A capacitor (smoothing capacitor), which smoothes a voltage supplied from the DC power source to the inverter circuit, is provided between the positive bus and the negative bus in parallel to the DC power source.
A main relay switch is provided between the DC power source and the smoothing capacitor. The main relay switch connects and disconnects the DC power source and the smoothing capacitor. Thus, the main relay switch connects and disconnects the DC power source and the inverter circuit.
A discharge switch is connected between the positive bus and the negative bus. The discharge switch is provided on the smoothing capacitor side relative to the main relay switch. The discharge switch connects and disconnects the positive electrode and the negative electrode of the smoothing capacitor.
When the main relay switch is turned on with the discharge switch being in the turned-off state, the output voltage of the DC power source is smoothed by the smoothing capacitor and supplied to the inverter circuit. The control circuit controls the six transistors of the inverter circuit to turn on and off, so that the inverter circuit outputs the three-phase AC currents to the stator coil of the three-phase synchronous motor based on the output voltage of the DC power source.
In an emergency situation, such as an abnormality or accident, the main relay switch is turned off to stop supply of the output voltage from the DC power source to the inverter circuit. In addition, the discharge switch is turned on to allow a current to flow from the positive electrode to the negative electrode of the smoothing capacitor through the discharge switch.
The electric charge stored in the smoothing capacitor is thus discharged. As a result, passengers in a vehicle are protected from being damaged by the electric charge stored in the smoothing capacitor even when the driving apparatus is broken by an accident or the like.
In some driving apparatuses for a three-phase AC synchronous motor having a stator coil, which is star-connected to a neutral point, a DC power source is not connected between a positive bus and a negative bus of the DC power source but is connected between the positive bus and the neutral point of the stator coil.
If the DC power source, the smoothing capacitor and the discharge switch are connected between the positive bus and the neutral point of the stator coil and a power supply capacitor is additionally connected between the positive bus and the negative bus, the power supply capacitor is not enabled to discharge because of the transistors forming the inverter circuit even when the discharge switch is turned on.
If the DC power source, the smoothing capacitor and the discharge switch are connected between the positive bus and the neutral point of the stator coil and a power supply capacitor is additionally connected between the neutral point of the stator coil and the negative bus, the power supply capacitor is not enabled to discharge similarly.
In another driving apparatus, the DC power source as well as the smoothing capacitor and the discharge switch are connected between the neutral point of the stator coil and the negative bus and a power supply capacitor is additionally connected between the positive bus and the negative bus. The power supply capacitor is not enabled to discharge similarly.
If the DC power source, the smoothing capacitor and the discharge switch are connected between the neutral point of the stator coil and the negative bus and a power supply capacitor is additionally connected between the positive bus and the neutral point of the stator coil, the power supply capacitor is not enabled to discharge similarly.